The invention relates to a method for absolute crankshaft angle determination of a rotating crankshaft of an internal combustion engine of a hand-held power tool, in particular, a portable hand-held power tool such as a motor chain saw, a cut-off machine, a trimmer, a blower, or the like. The internal combustion engine has a cylinder with a combustion chamber that is delimited by a piston driving a crankshaft. The crankshaft housing of the internal combustion engine is connected to the combustion chamber by at least one transfer passage whose transfer port opening into the combustion chamber is controlled by the piston. An ignition control unit is provided that triggers at the appropriate crankshaft angle an ignition spark at a spark plug correlated with the combustion chamber. An energy supply unit that is driven by the crankshaft for supplying electric energy for ignition is also provided.
The ignition device of an internal combustion engine in hand-held portable power tools has usually an induction coil that is arranged near magnets rotating with the crankshaft. For each revolution, voltage is generated in the induction coil. This voltage signal is approximately sine-shaped and has ideally three zero crossings. The voltage signal serves for electrically supplying the ignition device and provides the electric energy that is required for triggering the spark in a spark plug.
In order to determine the rotary position of the crankshaft, the precise mounting location of the induction coil as well as the rotational position of the revolving magnets relative to the crankshaft must be known. For example, if the fan wheel that supports the magnets is mounted on the crankshaft at an angular displacement, the generator signal will exhibit a matching angular displacement and this causes errors in the ignition timing. This error can be minimized by manual displacement of the induction coil. However, this requires appropriate adjusting labor; this is a complex task. Moreover, the occurring errors cannot be compensated always by positional changes of the induction coil because there is only limited space available about the circumference of the fan wheel for the induction coil.